1. Field of the Invention
This invention relates to triplet type objectives with a diaphragm arranged behind the lens system.
2. Description of the Prior Art
Triplet objectives with three components of positive, negative and positive powers from the front are well known. Because this type of lens offers a relatively high optical performance with a small number of lens elements, it has been widely used as a photographic lens for many years. Triplet objectives have also been used in so-called rear stop arrangements, namely, with a diaphragm in rear of the lens system. Such a rear stop type lens does not require moving the operating mechanism for the stop even when the entire lens system is moved to effect focusing. This affords the advantage of permitting the structure of the focusing mechanism to be simple.
Such rear stop type triplet objectives have been proposed, for example, in Japanese Patent Publications Nos. SHO 48-5494 and SHO 50-2807. However, these objectives have narrow total angular field coverages such as 55.degree.. Another objective proposed in Japanese Laid-Open Patent Publication No. SHO 57-2012 has relatively wide an angular field. However it is somewhat dark with an F-number of f/4. Also, because the ratio of the distance from the front vertex to the image plane to the focal length, or the so-called telephoto ratio assumes a value of greater than 1.1, the total length of the lens system is relatively long.